This application claims priority of European Patent Application No. 98306013.8, which was filed on Jul. 28, 1998.
This invention relates to communication systems and more particularly to a method and system for the fast closed loop power control in Wideband Code Division Multiple Access (W-CDMA) communications.
Traditionally, user traffic in a CDMA system is circuit switched and, 5 once a call has been set up, the connection is maintained throughout the duration of the service request. A Dedicated Traffic Channel (DTCH) is assigned to each active user for both the uplink and the downlink and each DTCH is characterized by a unique spreading code. Throughout the entire session, the DTCH is used exclusively by the active user.
The circuit switched method is robust and results in high system capacity by supporting macro-diversity (soft handover) power control. In wideband multiservice CDMA systems, extremely bursty traffic needs to be supported by adjusting the data rate, and hence the spreading factor and spreading code. However, the need to quickly adjust the spreading code leads to highly complex code allocation algorithms.
Another popular method for accommodating bursty services is through packet switched data. ETSI UMTS W-CDMA and ARIB W-CDMA propose to use the Random Access Channel (RACH) and the Forward Access Channel (FACH) to transmit infrequent bursty packet data. The advantage of such a scheme is a quick set up time, since dedicated channel is not required. However, this transmission mechanism uses open loop power control only, and macro-diversity is not supported.
In patent application Ser. No. EP 98303327.5 xe2x80x9cTime Division Multiple Access Communication Systemxe2x80x9d, multiplexing many bursty packet data users onto the same downlink DTCH was described. The multiplexing scheme combined many of the benefits of the above mentioned schemes, namely low complexity code allocation, macro-diversity and soft handover and low associated control overhead. In addition, the scheme provides limited closed loop power control. The extent to which the fast closed loop power control can be achieved depends upon radio frame configuration since the more slots allocated to a user in a radio frame, the better the closed power control. However, in the worst case, where only one slot is allocated to a user in one frame, closed loop power is slowed down and thus there is a significant performance hit.
There is thus a requirement for a fast closed loop power control to maintain packet data transmission performance.
According to a first aspect of the invention there is provided a packet switched communications system comprising a downlink communication channel over which a to station communicates with at least one user, said downlink communication channel being divided into a plurality of frames, each frame including a plurality of data packets, each data packet being directed to a predetermined user and including transmission power control information for said user, and characterized in that at least one data packet in every frame includes transmission power control information for at least one other user of the communication system.
The system may include a null user packet, not directed to any predetermined that includes transmission power control information for at least one user of the communication system. At least one packet (either data or null user) in every frame includes transmission power control information for at least one other user of the communication system.
According to a second aspect of the invention there is provided a method of packet switched communication between a station and at least one user comprising providing a downlink communication channel over which said station communicates with said at least one user, dividing said downlink communication channel into a plurality of frames, each frame including a plurality of data packets, directing each data packet to a predetermined user, including in each data packet transmission power control information for said user, and characterized in that at least one data packet in every frame includes transmission power control information for at least one other user of the communication system.
The system uses an Extended Transmission Power Control (ETPC) field, which contains packet transmission power control information for the other users of the packet switched communications system. This allows for very fast closed loop power control, since the power control information is updated once every frame, even once every packet, for packet transmission over shared single physical dedicated traffic channel. There is thus a significant capacity improvement.
Thus, a scheme to multiplex many bursty packet data users onto a single physical Dedicated Traffic Channel (DTCH) is provided. This scheme has advantages over both random access packet and single user per code virtual circuit transmission schemes for bursty packet data. The invention simplifies orthogonal spreading code allocation while maintaining most of the benefits of virtual circuit transmission (e.g., soft handover, diversity gain, and closed loop power control).